A gunman on a gray mountain bicycle robbed two pedestrians and tried to hold up a third waiting for a bus in Uniondale, all within 20 minutes on Tuesday morning, Nassau police said Friday.

Police want the public’s help in looking for the bicyclist who brandished a gun and stole money and a cellphone from a man, 43, who was walking south on Fenmore Avenue at 6:20 a.m., police said. The robber was last seen on Greengrove Avenue, police said.

Five minutes later, the same armed bicyclist held up another man, 32, walking west on Macon Place, pedaling off east with the victim’s money and cellphone, police said.

Then at 6:40 a.m., the robber displayed his gun again to another man, 27, at the bus stop on Uniondale Avenue and Macon Place, police said. But the victim ran south on Uniondale before anything was taken from him, authorities said.

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No injuries were reported.

The suspect was described as 6 feet tall, 25-30 years old and wearing dark pants, a hooded sweatshirt and a half mask, police said.

Detectives ask anyone with information to contact Nassau County Crime Stoppers at 800-244-TIPS.